1. Technical Field
The present invention relates to a projection system capable of changing the aspect ratio of a projected image and a projector including the projection system.
2. Related Art
As an aspect ratio converter used with a projection system of a projector, there is a front-mounted converter so disposed in front of a built-in projection system, that is, on the image side thereof that the converter is retrearably disposed.
A converter of this type is, however, provided as an external optical unit independent of a projector body, increases the size of the projector, and complicates adjustment of the entire projection system including the converter or greatly degrades a projected image.
There is another aspect ratio converter used with an image-taking system of a camera or any other similar apparatus instead of a projection system of a projector, that is, a rear-mounted relay system so disposed on the image side of an image formation system that the converter is removable from the image-taking system (see JP-A-2005-221597 and JP-A-2005-300928). The relay system is formed of a first group, a second group, and a third group, and the second group, which is the central group, is an anamorphic converter and can be inserted to and removed from the space between the first and third groups.
The relay system or the anamorphic converter disclosed in JP-A-2005-221597 or other patent documents, which is designed to be used with an image-taking system, can also be used with a projection system without any modifications but under a variety of restrictions.
A rear-mounted relay system, such as the one described above, is not designed to provide exact telecentricity. In a relay system of this type, telecentricity in a horizontal cross-sectional plane (X cross-sectional plane) and telecentricity in a vertical cross-sectional plane (Y cross sectional plane) are not satisfied at the same time in principle, which means that providing exact telecentricity in one of the X and Y cross-sectional planes greatly degrades telecentricity in the other cross-sectional plane, resulting in decrease in light usage efficiency or dependence thereof on direction.
When the image-taking system described in JP-A-2005-221597, which is essentially used with an interchangeable lens, is used without the rear-mounted relay system, an image formation system is directly fixed to an imaging unit and used alone. The rear-mounted relay system therefore needs to be long to maintain the performance of the image formation system. On the other hand, since no interchangeable lens is typically used with a projection system, a converter used with a projection system does not need to have a function as a general-purpose relay system or a general-purpose converter that allows a variety of interchangeable lenses to be mounted.